Mask material conversion

ABSTRACT

The dimensions of mask patterns, such as pitch-multiplied spacers, are controlled by controlled growth of features in the patterns after they are formed. To form a pattern of pitch-multiplied spacers, a pattern of mandrels is first formed overlying a semiconductor substrate. Spacers are then formed on sidewalls of the mandrels by depositing a blanket layer of material over the mandrels and preferentially removing spacer material from horizontal surfaces. The mandrels are then selectively removed, leaving behind a pattern of freestanding spacers. The spacers comprise a material, such as polysilicon and amorphous silicon, known to increase in size upon being oxidized. The spacers are oxidized to grow them to a desired width. After reaching the desired width, the spacers can be used as a mask to pattern underlying layers and the substrate. Advantageously, because the spacers are grown by oxidation, thinner blanket layers can be deposited over the mandrels, thereby allowing the deposition of more conformal blanket layers and widening the process window for spacer formation.

PRIORITY APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/932,993, filed Sep. 1, 2004.

REFERENCE TO RELATED APPLICATIONS

This application is related to the following: U.S. patent applicationSer. No. ______ to Abatchev et al., filed Aug. 31, 2004, entitledCritical Dimension Control, Attorney Docket No. MICRON.286A (Micron Ref.No. 03-1348.00/US); U.S. patent application Ser. No. ______ to Abatchevet al., entitled Method for Integrated Circuit Fabrication Using PitchMultiplication, Attorney Docket No. MICRON.294A (Micron Ref. No.03-1446.00/US); U.S. patent application Ser. No. ______ to Tran et al.,filed Aug. 31, 2004, entitled Methods for Increasing Photo-AlignmentMargins, Attorney Docket No. MICRON.295A (Micron Ref. No.04-0068.00/US); and U.S. patent application Ser. No. ______ to Sandhu etal., entitled Methods to Align Mask Patterns, Attorney Docket No.MICRON.296A (Micron Ref. No. 04-0114.00/US).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to integrated circuit fabrication and,more particularly, to masking techniques.

2. Description of the Related Art

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency inmodern electronics, integrated circuits are continuously being reducedin size. To facilitate this size reduction, the sizes of the constituentfeatures, such as electrical devices and interconnect line widths, thatform the integrated circuits are also constantly being decreased.

The trend of decreasing feature size is evident, for example, in memorycircuits or devices such as dynamic random access memories (DRAMs),static random access memories (SRAMs), ferroelectric (FE) memories, etc.To take one example, DRAM typically comprises millions of identicalcircuit elements, known as memory cells. In its most general form, amemory cell typically consists of two electrical devices: a storagecapacitor and an access field effect transistor. Each memory cell is anaddressable location that can store one bit (binary digit) of data. Abit can be written to a cell through the transistor and read by sensingcharge on the storage electrode from the reference electrode side. Bydecreasing the sizes of constituent electrical devices and theconducting lines that access them, the sizes of the memory devicesincorporating these features can be decreased. Additionally, storagecapacities can be increased by fitting more memory cells into the memorydevices.

The continual reduction in feature sizes places ever greater demands ontechniques used to form the features. For example, photolithography iscommonly used to pattern features, such as conductive lines, on asubstrate. The concept of pitch can be used to describe the size ofthese features. Pitch is defined as the distance between an identicalpoint in two neighboring features. These features are typically definedby spaces between adjacent features, which are typically filled by amaterial, such as an insulator or conductor. As a result, pitch can beviewed as the sum of the width of a feature and of the width of thespace separating that feature from a neighboring feature. Due to factorssuch as optics and light or radiation wavelength, however,photolithography techniques each have a minimum pitch below which aparticular photolithographic technique cannot reliably form features.Thus, the minimum pitch of a photolithographic technique can limitfeature size reduction.

“Pitch doubling” is one method proposed for extending the capabilitiesof photolithographic techniques beyond their minimum pitch. Such amethod is illustrated in FIGS. 1A-1F and described in U.S. Pat. No.5,328,810, issued to Lowrey et al., the entire disclosure of which isincorporated herein by reference. With reference to FIG. 1A,photolithography is first used to form a pattern of lines 10 in aphotoresist layer overlying a layer 20 of an expendable material and asubstrate 30. As shown in FIG. 1B, the pattern is then transferred by anetch step (preferably anisotropic) to the layer 20, formingplaceholders, or mandrels, 40. The photoresist lines 10 can be strippedand the mandrels 40 can be isotropically etched to increase the distancebetween neighboring mandrels 40, as shown in FIG. 1C. A layer 50 ofmaterial is subsequently deposited over the mandrels 40, as shown inFIG. 1D. Spacers 60, i.e., material extending or originally formedextending from sidewalls of another material, are then formed on thesides of the mandrels 40 by preferentially etching the spacer materialfrom the horizontal surfaces 70 and 80 in a directional spacer etch, asshown in FIG. 1E. The remaining mandrels 40 are then removed, leavingbehind only the spacers 60, which together act as an etch mask forpatterning underlying layers, as shown in FIG. 1F. Thus, where a givenpitch formerly included a pattern defining one feature and one space,the same width now includes two features and two spaces defined by thespacers 60. As a result, the smallest feature size possible with aphotolithographic technique is effectively decreased.

It will be appreciated that while the pitch is actually halved in theexample above, this reduction in pitch is conventionally referred to aspitch “doubling,” or, more generally, pitch “multiplication.” That is,conventionally “multiplication” of pitch by a certain factor actuallyinvolves reducing the pitch by that factor. The conventional terminologyis retained herein.

The critical dimension of a feature is the feature's minimum dimension.For features formed using the spacers 60, the critical dimensiontypically corresponds to the width of the spacers. The width of thespacers, in turn, is typically dependent upon a thickness 90 (see FIGS.1D and 1E) of the layer 50. Thus, the layer 50 is typically formed to athickness 90 corresponding to the desired critical dimension.

The quality and uniformity of the spacers 60 directly affect the qualityof the integrated circuits partially defined in the substrate 30 usingthe spacers as a mask. Where the desired spacers 60 are relatively widecompared to the mandrels 40 and/or the space separating the spacers 60,however, it has been observed that the resulting spacers 60 and the etchmask resulting from the spacers 60 can have poor uniformity. This pooruniformity, in turn, can cause poorly defined and non-uniform featuresto be formed in the substrate. As a result, the electrical performanceof integrated circuits formed in the substrate may be degraded or theintegrated circuits may be unusable.

Accordingly, there is a need for methods of forming etch masks havinghighly uniform and well-defined patterns, especially in conjunction withspacers formed in pitch multiplication.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method is provided forfabricating an integrated circuit. The method comprises providing asubstrate having an overlying mask layer. The mask layer comprises maskmaterial and openings which form a pattern. The mask material isoxidized and the pattern is subsequently transferred to the substrate.

According to another aspect of the invention, a process is provided forforming an integrated circuit. The process comprises providing a patterncomprising a plurality of mask lines in a mask layer overlying asubstrate. The mask lines comprise a precursor material. The mask linesare grown to a desired width by chemically reacting the precursormaterial to form a chemical compound occupying a larger volume than theprecursor material.

According to another aspect of the invention, a process is provided forforming an integrated circuit. The process comprises providing apatterned mask layer overlying a substrate. The mask layer comprises aprecursor material which is chemically reacted to form an etch stopmaterial. The pattern in the mask layer is subsequently transferred toan underlying layer.

According to yet another aspect of the invention, a method ofsemiconductor processing is provided. The method comprises providing asubstrate. A temporary layer overlies the substrate and a photodefinablelayer overlies the temporary layer. A pattern is formed in thephotodefinable layer and transferred to the temporary layer to form aplurality of placeholders in the temporary layer. A blanket layer ofspacer material is deposited over the plurality of placeholders. Thespacer material is selectively removed from horizontal surfaces. Theplaceholders are selectively removed relative to the spacer material.The spacer material is expanded to a desired size.

According to another aspect of the invention, a process is provided forforming a memory device. The process comprises forming a plurality ofmask lines by pitch multiplication. Neighboring mask lines are separatedfrom one another by an open space and the open space between neighboringmask lines is narrowed.

According to yet another aspect of the invention, a method is providedfor semiconductor processing. The method comprises forming a pluralityof mask lines by pitch multiplication. A volume of material forming themask lines is expanded to a desired width by converting the material toan other material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIGS. 1A-1F are schematic, cross-sectional side views of mask lines,formed in accordance with a prior art pitch multiplication method;

FIG. 2 is a schematic, cross-sectional side view of a partially formedmemory device, in accordance with preferred embodiments of theinvention;

FIG. 3 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 2 after forming lines in a photo-definable layer,in accordance with preferred embodiments of the invention;

FIG. 4 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 3 after widening spaces between photoresist lines,in accordance with preferred embodiments of the invention;

FIG. 5 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 6 after etching through a hard mask layer, inaccordance with preferred embodiments of the invention;

FIG. 6 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 5 after transferring a pattern from thephotoresist and hard mask layers to a temporary layer, in accordancewith preferred embodiments of the invention;

FIG. 7 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 6 after depositing a blanket layer of a spacermaterial, in accordance with preferred embodiments of the invention;

FIG. 8 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 7 after a spacer etch, in accordance withpreferred embodiments of the invention;

FIG. 9 is a schematic, cross-sectional side view of the partially formedmemory device of FIG. 8 after being coated with a removable material, inaccordance with preferred embodiments of the invention;

FIG. 10 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 9 after etching the photoresist and hardmask layers, in accordance with preferred embodiments of the invention;

FIG. 11 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 10 after removing the photoresist andtemporary layers, in accordance with preferred embodiments of theinvention;

FIG. 12 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 11 after enlarging the spacers to a desiredwidth, in accordance with preferred embodiments of the invention;

FIG. 13 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 12 after transferring the spacer pattern toan underlying hard mask layer, in accordance with preferred embodimentsof the invention;

FIG. 14 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 13 after removing the spacers, inaccordance with preferred embodiments of the invention;

FIG. 15 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 1 having an additional masking layer, inaccordance with preferred embodiments of the invention;

FIG. 16 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 15 after forming spacers, in accordancewith preferred embodiments of the invention;

FIG. 17 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 16 after expanding spacers, in accordancewith preferred embodiments of the invention;

FIG. 18 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 17 after etching through a hard mask layer,in accordance with preferred embodiments of the invention;

FIG. 19 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 18 after transferring the spacer pattern tothe additional masking layer, in accordance with preferred embodimentsof the invention;

FIG. 20 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 6 after depositing a blanket layer of aspacer material, in accordance with other preferred embodiments of theinvention;

FIG. 21 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 20 after enlarging the blanket layer to adesired thickness, in accordance with other preferred embodiments of theinvention; and

FIG. 22 is a schematic, cross-sectional side view of the partiallyformed memory device of FIG. 21 after removing the hard mask andtemporary layers, in accordance with other preferred embodiments of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has been found that the poor quality of some spacer patterns is dueto difficulties depositing conformal layers of spacer material and/oretching this material to form spacers. Because spacers are typicallyformed out of the vertically extending parts of blanket layers of spacermaterial over a complex mask topography, the conformality of the layerswill affect the uniformity, e.g., the widths, the heights and thephysical placement, of the spacers formed from the layers. It will beappreciated that the more conformal a layer is, the more closely itreplicates the shape of the surface on which it is deposited.

As critical dimensions continue to decrease, however, the aspect ratiosof the spaces, or openings, between mandrels continue to increase. Thisis partly due to the desire to pack features more closely together byreducing the widths of the spaces between mandrels. In addition, incommon methods of transferring patterns, both the spacers and anunderlying layer are exposed to an etchant, which preferentially etchesaway the substrate material. The etchants, however, also wear away thespacers, albeit at a slower rate. Thus, even as critical dimensionsdecrease, the vertical heights of the spacers must remain at a levelthat allow a pattern transfer to be completed before the spacers arecompletely worn away by etchants.

Accordingly, deposition of highly conformal layers of spacer materialcan be increasingly difficult, due in part to increasingly limiteddiffusion of precursor gases into the bottom portions of the spacesbetween mandrels. This diffusion becomes increasingly more limitedduring the course of a deposition, as sidewalls fill in with spacermaterial, thereby further increasing the aspect ratios of the spacebetween the sidewalls. For this reason, relatively thin layers are moreeasily and reliably deposited than relatively thick layers. As a resultof poor conformality of relatively thick deposited layers, theuniformity of spacers formed from the layers can be also be poor.

In addition, just as it may be difficult for precursors to reach thebottoms of high aspect ratio spaces, the aspect ratios of some spacescan also limit the amount of etchant that penetrates to the bottoms ofthose spaces. Consequently, when etching laterally extending parts ofthe layer of spacer material to define individual spacers, some spacermaterial may undesirably remain at the bottoms of these spaces, causingthe formation of spacers having bottom surfaces with widths differentfrom expected widths. Thus, difficulties in depositing and also etchinglayers of spacer materials make precise control over the widths of thespacers difficult.

Advantageously, preferred embodiments of the invention allow for moreprecise control over the widths and uniformity of features formed usinga mask pattern. In the preferred embodiments, the mask pattern is formedwith a material that can itself be increased to a desired size orcritical dimension by a subsequent process, such as oxidation. The maskpattern is then subjected to the expansion process to increase thewidths of mask features to a desired width. The now-enlarged maskfeatures can then be used to form a pattern in an underlying layer. Asused herein, it will be appreciated that a “feature” refers to anyvolume or opening formed in a material, e.g., in a mask layer or in thesubstrate, and having discrete boundaries.

Preferably, the pattern subjected to the enlargement process is apattern of spacers formed by pitch multiplication. The spacerspreferably comprise silicon, e.g., polysilicon or amorphous silicon. Theenlargement process can be any process that causes the spacers toexpand. Where the spacers comprise silicon, the expansion processpreferably comprises oxidation of the spacers to form silicon oxide.Moreover, the spacers are oxidized until they grow to a desired width.After growing to the desired width, the spacers can be used to patternfeatures in underlying layers. Optionally, the spacers can be trimmed toa desired critical dimension after being oxidized.

Advantageously, by growing the spacers to a desired width after they areformed, a thinner layer of spacer material can be deposited. Bydepositing thinner layers than would otherwise be required for a desiredcritical dimension, the conformality of the layers is less dependentupon the limitations of the deposition and/or etching process. As aresult, the process window for forming spacers of a given criticaldimension is widened.

In addition, as noted above, a spacer is typically formed to aparticular height that is dictated in part by the requirements of aparticular semiconductor process to be performed through the mask (e.g.,etching, implantation, doping, oxidation, etc.) and particular materialsof the underlying substrate that are to be exposed to the process. Forexample, spacers are typically formed to a height that accounts for theremoval of some material during subsequent etching of an underlyinglayer. Advantageously, because spacers typically grow both laterally andvertically during, e.g., oxidation, the resulting taller spacers areless likely to be etched away when transferring the spacer pattern to anunderlying layer. Also, because the initial height of the spacer formedby a spacer etch is dependent on the height of a mandrel, the mandrel'sheight can be less than the height that would be required if the spacerswere not later enlarged. Consequently, because the height of themandrels can be reduced, the aspect ratio of the spaces between themandrels is also reduced, thereby further easing the requirements forthe spacer material deposition and further increasing the processwindow.

It will be appreciated that silicon nitrides and silicon oxides areparticularly suitable as spacer materials for mask formation, due inpart to the availability of selective etch chemistries relative to avariety of other materials, including metals, oxides andsilicon-containing substrates. Advantageously, the conversion of thesilicon spacer into a silicon oxide allows preferred embodiments of theinvention to be easily inserted into various process flows, especiallyfor pitch multiplication, without needing to substantially alter theprocess flow. In addition, partial conversion of silicon spacers tosilicon oxide still allows selective etch chemistries that will attack,e.g., a carbon mask material without attacking either silicon oxide orresidual silicon.

Reference will now be made to the Figures, wherein like numerals referto like parts throughout. It will be appreciated that FIGS. 2-22 are notnecessarily drawn to scale.

It will be also appreciated that, while the preferred embodiments willfind application in any context in which it may be desirable to increasethe size of the individual parts constituting a mask pattern after thoseparts are formed, in particularly advantageous embodiments the maskpattern comprises spacers formed by pitch multiplication. Thus, thepitch multiplied features preferably have a pitch below the minimumpitch of the photolithographic technique used for patterning themandrels used to form the spacers. In addition, while the preferredembodiments can be used to form any integrated circuit, they areparticularly advantageously applied to form devices having arrays ofelectrical devices, including logic or gate arrays and volatile andnon-volatile memory devices such as DRAM, ROM or flash memory.

With reference to FIG. 2, a partially formed integrated circuit 100 isprovided. A substrate 110 is provided below various masking layers120-150. The layers 120-150 will be etched to form a mask for patterningthe substrate 110 to form various features, as discussed below.

It will be appreciated that the “substrate” can include a layer of asingle material, a plurality of layers of different materials, a layeror layers having regions of different materials or structures in them,etc. These materials can include semiconductors, insulators, conductors,or combinations thereof. For example, the substrate can comprise dopedpolysilicon, an electrical device active area, a silicide, or a metallayer, such as a tungsten, aluminum or copper layer, or a combinationthereof. Thus, the mask features discussed below can directly correspondto the desired placement of conductive features, such as interconnects,in the substrate. In other embodiments, the substrate can be aninsulator and the location of mask features can correspond to thedesired location of insulators.

The materials for the layers 120-150 overlying the substrate 110 arepreferably chosen based upon consideration of the chemistry and processconditions for the various pattern forming and pattern transferringsteps discussed herein. Because the layers between a topmostphotodefinable layer 120 and the substrate 110 will function to transfera pattern derived from the photodefinable layer 120 to the substrate110, the layers between the photodefinable layer 120 and the substrate110 are preferably chosen so that they can be selectively etchedrelative to other exposed materials. It will be appreciated that amaterial is considered selectively, or preferentially, etched when theetch rate for that material is at least about 5 times greater,preferably about 10 times greater and more preferably about 20 timesgreater than that for surrounding materials.

In the illustrated embodiment, the photodefinable layer 120 overlies afirst hard mask, or etch stop, layer 130, which overlies a temporarylayer 140, which overlies a second hard mask, or etch stop, layer 150,which overlies the substrate 110 to be patterned, e.g., by etchingthrough the second hard mask layer 150.

The photodefinable layer 120 is preferably formed of a photoresist,including any photoresist known in the art. For example, the photoresistcan be any photoresist compatible with 157 nm, 193 nm or 248 nmwavelength systems, 193 nm wavelength immersion systems or electron beamsystems. Examples of preferred photoresist materials include argonfluoride (ArF) sensitive photoresist, i.e., photoresist suitable for usewith an ArF light source, and krypton fluoride (KrF) sensitivephotoresist, i.e., photoresist suitable for use with a KrF light source.ArF photoresists are preferably used with photolithography systemsutilizing relatively short wavelength light, e.g., 193 nm. KrFphotoresists are preferably used with longer wavelength photolithographysystems, such as 248 nm systems.

The material for the first hard mask layer 130 preferably comprises aninorganic material, and exemplary materials include silicon oxide(SiO₂), silicon or a dielectric anti-reflective coating (DARC), such asa silicon-rich silicon oxynitride. In the illustrated embodiment, thefirst hard mask layer 130 is a dielectric anti-reflective coating(DARC). The temporary layer 140 is preferably formed of amorphouscarbon, which offers very high etch selectivity relative to thepreferred hard mask materials. More preferably, the amorphous carbon isa form of amorphous carbon that is highly transparent to light and whichoffers further improvements in alignment. Deposition techniques forforming a highly transparent carbon can be found in A. Helmbold, D.Meissner, Thin Solid Films, 283 (1996) 196-203, the entire disclosure ofwhich is incorporated herein by reference.

Because the preferred chemistries for etching photoresist also typicallyetch significant amounts of amorphous carbon and because chemistries areavailable for etching amorphous carbon with excellent selectivityrelative to a variety of non-photoresist materials, the hard mask layer130, selected from such materials, preferably separates the layers 120and 140. As noted above, the first hard mask layer 130 preferablycomprises silicon oxide, silicon or a DARC, which can be preferentiallyremoved relative to amorphous carbon.

In addition, using DARCs for the first hard mask layer 130 can beparticularly advantageous for forming patterns having pitches near theresolution limits of a photolithographic technique. The DARCs canenhance resolution by minimizing light reflections, which can decreasethe precision with which photolithography can define the edges of apattern. Optionally, a bottom anti-reflective coating (BARC) (not shown)can similarly be used in addition to the first hard mask layer 130 tocontrol light reflections.

The second hard mask layer 150 preferably comprises a dielectricanti-reflective coating (DARC) (e.g., a silicon oxynitride), silicon oraluminum oxide (Al₂O₃). In addition, a bottom anti-reflective coating(BARC) (not shown) can optionally be used to control light reflections.In the illustrated embodiment, the second hard mask layer 150 comprisesAl₂O₃.

In addition to selecting appropriate materials for the various layers,the thicknesses of the layers 120-150 are preferably chosen dependingupon compatibility with the etch chemistries and process conditionsdescribed herein. For example, when transferring a pattern from anoverlying layer to an underlying layer by selectively etching theunderlying layer, materials from both layers are removed to some degree.Thus, the upper layer is preferably thick enough so that it is not wornaway over the course of the pattern transfer.

In the illustrated embodiment, the photodefinable layer 120 ispreferably between about 100 nm and about 300 nm thick and, morepreferably, between about 150 nm and about 250 nm thick. The first hardmask layer 130 is preferably between about 10 nm and about 500 nm thickand, more preferably, between about 15 nm and about 300 nm thick. Thetemporary layer 140 is preferably between about 100 nm and about 300 nmthick and, more preferably, between about 100 nm and about 200 nm thick.The second hard mask layer 150 is preferably between about 10 nm andabout 50 nm thick and, more preferably, between about 10 nm and about 30nm thick.

It will be appreciated that the various layers discussed herein can beformed by various methods known to those of skill in the art. Forexample, various vapor deposition processes, such as chemical vapordeposition, can be used to form hard mask layers. Spin-on-coatingprocesses can be used to form photodefinable layers. In addition,amorphous carbon layers can be formed by chemical vapor deposition usinga hydrocarbon compound, or mixtures of such compounds, as carbonprecursors. Exemplary precursors include propylene, propyne, propane,butane, butylene, butadiene and acetelyne. A suitable method for formingamorphous carbon layers is described in U.S. Patent No. 6,573,030 B1,issued to Fairbairn et al. on Jun. 3, 2003, the entire disclosure ofwhich is incorporated herein by reference.

In a first phase of methods in accordance with the preferred embodimentsand with reference to FIGS. 3-11, a pattern of spacers is formed bypitch multiplication.

With reference to FIG. 3, a pattern comprising spaces or trenches 122delimited by photodefinable material features 124 is formed in thephotodefinable layer 120. The trenches 122 can be formed by, e.g.,photolithography, in which the layer 120 is exposed to radiation througha reticle and then developed. After being developed, the remainingphotodefinable material, photoresist in the illustrated embodiment,forms features such as the illustrated lines 124 (shown in cross-sectiononly).

The pitch of the resulting lines 124 and spaces 122 is equal to the sumof the width of a line 124 and the width of a neighboring space 122. Tominimize the critical dimensions of features formed using this patternof lines 124 and spaces 122, the pitch is preferably at or near thelimits of the photolithographic technique used to pattern thephotodefinable layer 120. Thus, the pitch may be at the minimum pitch ofthe photolithographic technique and the spacer pattern discussed belowcan advantageously have a pitch below the minimum pitch of thephotolithographic technique.

As shown in FIG. 4, the spaces 122 can optionally be widened by etchingthe photoresist lines 124, to form modified spaces 122 a and lines 124a. The photoresist lines 124 are preferably etched using an isotropicetch, such as a sulfur oxide plasma, e.g., a plasma comprising SO₂, O₂,N₂ and Ar. The extent of the etch is preferably selected so that thewidths of the spaces 122 a and the lines 124 a are substantially equalto the desired spacing between the later-formed spacers, as will beappreciated from the discussion of FIGS. 8-10 below. Advantageously,this etch allows the lines 124 a to be narrower than would be possiblewith using the photolithographic technique used to pattern thephotodefinable layer 120. In addition, the etch can smooth the edges ofthe lines 124 a, thus improving the uniformity of those lines 124 a.

The pattern in the (modified) photodefinable layer 120 is preferablytransferred to the temporary layer 140 to allow for deposition of alayer 170 of spacer material (FIG. 7). Thus, the temporary layer 140 ispreferably formed of a material that can withstand the processconditions for spacer material deposition, discussed below. In otherembodiments where the deposition of spacer material is compatible withthe photodefinable layer 120, the temporary layer 140 can be omitted andthe spacer material can be deposited directly on the photo-definedfeatures 124 or the modified photodefined features 124 a of thephotodefinable layer 120 itself.

In the illustrated embodiment, in addition to having higher heatresistance than photoresist, the material forming the temporary layer140 is preferably selected such that it can be selectively removedrelative to the material for the spacers 175 (FIGS. 8) and theunderlying etch stop layer 150. As noted above, the layer 140 ispreferably formed of amorphous carbon.

The pattern in the photodefinable layer 120 is preferably firsttransferred to the hard mask layer 130, as shown in FIG. 5. Thistransfer is preferably accomplished using an anisotropic etch, such asan etch using a fluorocarbon plasma, although a wet (isotropic) etch mayalso be suitable if the hard mask layer 130 is thin. Preferredfluorocarbon plasma etch chemistries include CF₄, CFH₃, CF₂H₂ and CF₃H.

The pattern in the photodefinable layer 120 is then transferred to thetemporary layer 140, as shown in FIG. 6, preferably using aSO₂-containing plasma, e.g., a plasma containing SO₂, O₂ and Ar.Advantageously, the SO₂-containing plasma can etch carbon of thepreferred temporary layer 140 at a rate greater than 20 times and, morepreferably, greater than 40 times the rate that the hard mask layer 130is etched. A suitable SO₂-containing plasma is described in U.S. patentapplication Ser. No. ______ of Abatchev et al., filed Aug. 31, 2004,entitled Critical Dimension Control, Attorney Docket No. MICRON.286A(Micron Ref. No. 03-1348.00/US), the entire disclosure of which isincorporate herein by reference. It will be appreciated that theSO₂-containing plasma can simultaneously etch the temporary layer 140and also remove the photodefinable layer 120. The resulting lines 124 bconstitute the placeholders or mandrels with which a pattern of spacers175 (FIG. 8) will be formed.

Next, as shown in FIG. 7, a layer 170 of spacer material is preferablyblanket deposited conformally over exposed surfaces, including the hardmask layer 130, the hard mask 150 and the sidewalls of the temporarylayer 140. Optionally, the hard mask layer 130 can be removed beforedepositing the layer 170. The spacer material can be any material thatcan act as a mask for transferring a pattern to the underlying substrate110, or that otherwise can allow processing of underlying structuresthrough the mask being formed. The spacer material preferably: 1) can bedeposited with good step coverage; 2) can be deposited at a temperaturecompatible with the temporary layer 140; 3) can be further processed toenlarge its dimensions; and 4) can be selectively etched relative to thetemporary layer 140 and any layer underlying the temporary layer 140after being enlarged. Preferred materials include polysilicon andamorphous silicon. The layer 170 is preferably deposited to a thicknessof between about 20 nm to about 60 nm and, more preferably, about 20 nmto about 50 nm. Preferably, the step coverage is about 80% or greaterand, more preferably, about 90% or greater.

As shown in FIG. 8, the spacer layer 170 is then subjected to ananisotropic etch to remove spacer material from horizontal surfaces 180of the partially formed integrated circuit 100. Such an etch, also knownas a spacer etch, can be performed using HBr/Cl plasma. The etch caninclude a physical component and preferably also includes a chemicalcomponent, e.g., a reactive ion etch (RIE), such as a Cl₂, HBr etch.Such an etch can be performed, for example, using a LAM TCP9400 flowingabout 0-50 sccm Cl₂ and about 0-200 sccm HBr at about 7-60 mTorrpressure with about 300-1000 W top power and about 50-250 W bottompower.

The hard mask layer 130 (if still present) and the temporary layer 140are next removed to leave free standing spacers 175 (FIG. 11). Becausethe spacers 175 may be thin and because the hard mask layer 130 may beformed of a material similar to the spacers 175, a space-fill layer 155may be formed over and around the spacers 175 to help maintain thestructural integrity of the spacers 175 and to aid in etching the layers130 and 140, as shown in FIG. 9. Preferably, the layer 155 comprisesphotoresist, which can be deposited in a spin-on process. In otherembodiments, e.g., where the spacers 175 are sufficiently wide and whereadequate etch chemistries are available, the layers 130 and 140 may beremoved without deposition of the layer 155.

With reference to FIG. 10, the hard mask layer 130, along with a topportion of the space-fill layer 155, is removed, for example, byplanarization. Preferred chemistries for etching the layers 130 and 155include a two step etch: first using CF₄/He plasma until the layer 130(FIG. 9) is removed and then using an O₂ plasma to remove the temporarylayer 140, along with a remaining portion of the space-fill layer 155.The resulting structure is shown in FIG. 11. Alternatively, to removethe layer 130 in the first part of the etch, the layers 130 and 155 canbe subjected to chemical mechanical polishing.

Thus, a pattern of freestanding spacers 175 is formed. Preferredchemistries for etching the layers 140 and 155 include a sulfur oxideplasma etch. Advantageously, silicon is more readily etched, eitherisotropically and anisotropically, than materials, such as siliconnitrides or silicon oxides, that are typically used for spacers. In someembodiments, the critical dimension of the spacers 175 is adjusted afterthe spacer etch by trimming the spacers 175.

Thus, pitch multiplication has been accomplished. In the illustratedembodiment, the pitch of the spacers 175 is roughly half that of thephotoresist lines 124 (FIG. 3) originally formed by photolithography.Advantageously, spacers 175 having a pitch of about 100 nm or less canbe formed. It will be appreciated that because the spacers 175 areformed on the sidewalls of the features or lines 124 b, the spacers 175generally follow the outline of the pattern of features or lines 124originally formed in the photodefinable layer 120.

Next, in a second phase of methods according to the preferredembodiments, the spacers 175 are enlarged so that their widthscorrespond to the desired critical dimensions of features that are to beformed in the substrate 110. Preferably, this enlargement isaccomplished by reacting the spacers 175 to form a new compound or alloyoccupying more space. In the illustrated embodiment having spacersformed of silicon, the enlargement process preferably comprisesoxidation of the spacers. It will be appreciated that the spacers 175grow upon being oxidized, as shown in FIG. 12. The size of the spacers175 a will vary depending upon the extent to which the spacers 175 areoxidized. Thus, the duration and degree of the oxidation is preferablychosen so that the spacers 175 reach a desired width 95. The oxidationof the spacers 175 can be accomplished by any oxidation process known inthe art, including thermal oxidation, oxidation using oxygen radicals orplasma, etc. In other embodiments, the spacers 175 can be enlarged bybeing nitrided by any nitridation process known in the art. Thus, apattern of spacers 175 a having desired widths 95 can be formed.

It will be appreciated that the spacers 175 can be formed of anymaterial that can be expanded, can be conformally deposited and forwhich suitable etch chemistries are available. For example, the spacers175 can be formed using titanium and can be enlarged by oxidation ornitridation to form TiO₂ or TiN₂. Other examples of materials includetantalum (which can be expanded by oxidation or nitridation to formtantalum oxide or tantanlum nitride) and tungsten (which can be expandedby oxidation or nitridation to form tungsten oxide or tungsten nitride).

Preferably, the extent of the enlargement is chosen such that thespacers 175 are enlarged to a width substantially equal to the desiredcritical dimension of the features, such as interconnects, word lines,bit lines, transistor rows, or gaps between damascene lines, which willbe patterned in the substrate 110 using the pattern formed by thespacers 175 a. For example, the spacers 175 a can be oxidized to agreater or less extent, depending upon whether the desired criticaldimensions are only slightly or more substantially greater than thedimensions of the non-oxidized spacers 175. Thus, process conditions,such as duration, chemical reactivity, temperature, etc., are chosen toachieve the desired degree of spacer expansion.

It will be appreciated that growth of the spacers 175 will also narrowthe space separating those spacers 175. Preferably, the spacers 175 arepositioned to account for this narrowing. In addition, the criticaldimension of the spacers 175 a can adjusted after the expansion bytrimming the spacers 175 a, e.g., with an isotropic etch.

It will also be appreciated that the spacers 175 a themselves may beused directly as a hard mask to pattern an underlying substrate 110.Preferably, however, the pattern of the spacers 175 a is transferred toone or more underlying layers which offer better etch selectivity to thesubstrate 110 than the spacers 175 a. With reference to FIG. 13, thepattern made out by the spacers 175 a can be transferred to the secondhard mask layer 150. Preferably, the second hard mask layer 150 isetched using a BCl₃/Cl₂ plasma etch.

With reference to FIG. 14, the spacers 175 a can optionally be removedbefore patterning the substrate 110. The spacers 175 a can be removedusing a wet etch process. Advantageously, by removing the spacers 175 a,the aspect ratio of the mask overlying the substrate 110 is reduced,thereby allowing etchants other processing chemicals to more easilyreach the substrate and, so, improving the formation of verticalsidewalls or otherwise clearly delineating and completing processing.

In other embodiments, as shown in FIG. 15, an additional mask layer 160can be utilized to pattern difficult to pattern substrates 110. Suchsubstrates can include, for example, multiple layers, which requiremultiple successive etches to pattern. Due to the availability ofchemistries that allow very selective removal of amorphous carbonrelative to many silicon-containing substrate materials, the additionalmask layer 160 is preferably formed of amorphous carbon.

It will be appreciated that the steps discussed above may be applied toform spacers 175 a overlying the additional mask layer 160. Withreference to FIG. 16, a pattern of spacers 175 is formed. As shown inFIG. 17, the spacers 175 are then expanded, by, e.g., oxidation, to adesired width, as discussed above. The pattern of spacers 175 a can thenbe transferred to the second hard mask layer 150, preferably using aBCl₃/Cl₂ plasma etch, as shown in FIG. 18. The pattern is thentransferred to the additional mask layer 160, preferably byanisotropically etching the additional mask layer 160, as shown in FIG.19. Preferably, the anisotropic etch is comprises exposing theadditional mask layer 160 to a SO₂-containing plasma. In otherembodiments, it will be appreciated that the spacers 175 may be removedbefore etching the layer 150 or before etching the substrate 110, asdiscussed above with respect to FIG. 14.

The substrate 110 can then be processed through the mask layers 160 and150 and the spacers 175 a to define various features, e.g., transistors,capacitors and/or interconnects. Where the substrate 110 compriseslayers of different materials, a succession of different chemistries,preferably dry-etch chemistries, can be used to successively etchthrough the different layers. It will be appreciated that, dependingupon the chemistry or chemistries used, the spacers 175 a and the hardmask layer 150 may be etched. Amorphous carbon of the additional masklayer 160, however, advantageously offers excellent resistance toconventional etch chemistries, especially those used for etchingsilicon-containing materials. Accordingly, the additional mask layer 160can effectively be used as a mask for etching through a plurality ofsubstrate layers, or for forming high aspect ratio trenches. Theadditional mask layer 160 can later be removed for further processing ofthe substrate 110.

It will be appreciated that, in any of the steps described herein,transferring a pattern from a first level to a second level involvesforming features in the second level that generally correspond tofeatures on the first level. For example, the path of lines in thesecond level will generally follow the path of lines on the first leveland the location of other features on the second level will correspondto the location of similar features on the first level. The preciseshapes and sizes of features can vary from the first level to the secondlevel, however. For example, depending upon etch chemistries andconditions, the sizes of and relative spacings between the featuresforming the transferred pattern can be enlarged or diminished relativeto the pattern on the first level, while still resembling the sameinitial “pattern.” Thus, the transferred pattern is still considered tobe the same pattern as the initial pattern. In contrast, forming spacersaround mask features can change the pattern.

It will be appreciated that formation of contacts according to thepreferred embodiments offers numerous advantages. For example, becausethinner layers are more easily conformally deposited than thickerlayers, the layers of spacer material from which spacers are formed canbe deposited with improved conformality. As a result, spacers can beformed from these layers with improved uniformity. Moreover, therelative thinness of these layers reduces the aspect ratios of trencheslined with the blanket layer of spacer material, thereby allowingetchants to more easily penetrate to the bottom of the trenches and,thus, facilitating the spacer etch.

It will also be appreciated that various modifications of theillustrated embodiments are possible. For example, the pitch of thespacers 175 or 175 a can be more than doubled. Further pitchmultiplication can be accomplished by forming additional spacers aroundthe spacers 175 or 175 a, then removing the spacers 175 or 175 a, thenforming spacers around the spacers that were formerly around the spacersthe 175 or 175 a, and so on. An exemplary method for further pitchmultiplication is discussed in U.S. Pat. No. 5,328,810 to Lowrey et al.

In addition, various other patterns, for patterning features ofdifferent sizes, can be overlaid or formed adjacent to the spacers 175or 175 a. For example, an additional photodefinable layer can be formedoverlying the spacers 175 or 175 a and then patterned to form the otherpatterns. Methods for forming such patterns are disclosed in U.S. patentapplication Ser. No. ______ of Tran et al., filed Aug. 31, 2004,entitled Methods for Increasing Photo-Alignment Margins, Attorney DocketNo. MICRON.295A (Micron Ref. No. 04-0068.00/US), the entire disclosureof which is incorporated herein by reference.

Moreover, while all the spacers 175 can be oxidized to have a similarwidth, in other embodiments, only some of the spacers 175 may beoxidized. For example, some spacers 175 can be protected from oxidationby depositing and patterning a protective layer (for which selectiveetch chemistries are available) and then oxidizing exposed spacers.

In addition, depending upon the material being converted and the extentof the conversion process, the oxidation or subsequent chemicalconversion process may not appreciably increase the size of the spacers175. In such case, the processes disclosed herein can nevertheless beapplied to convert the spacers 175 to a material for which highlyselective etch chemistries are available. As such, the conversionprocess can advantageously convert the spacers 175 to a better etch stopfor subsequent etch steps. For example, a mask precursor material can beconverted to a silicon or metal oxide or nitride, which canadvantageously provide good etch selectivity to surrounding, i.e.,underlying, materials.

With reference to FIGS. 20-22, where the spacers 175 are enlarged, itwill be appreciated that the spacers 175 or the layer 170 can beenlarged, e.g., by oxidation, at any point after deposition of thespacer material and before forming the free-standing spacers 175. Forexample, after depositing a blanket layer of spacer material 170 (FIG.20), the entire blanket layer 170 can be expanded, as shown in FIG. 21to form an expanded blanket layer 170 a. As noted above, the expansionprocess, including process conditions (e.g., duration, chemicalreactivity, temperature, etc.), is preferably chosen such that theblanket layer 170 expands to a desired thickness corresponding to adesired critical dimension, taking into account any horizontal shrinkageduring the subsequent spacer etch. Thus, the expansion process may leavethe layer 170 only partially oxidized. As shown in FIG. 22, after aspacer etch, the mandrels 124 b are then removed to leave thefree-standing spacers 175 a. Advantageously, because the spacers 175 aare thicker than the spacers 175, a protective space-fill layer 155(FIG. 9) may not necessary and the mandrels 124 b can be etched using ananisotropic etch, e.g., using a fluorocarbon plasma.

In other embodiments, the spacers 175 can be expanded after the spaceretch and before etching the mandrels (e.g., the spacers 175 in the FIG.8 can be expanded). Advantageously, because the spacers 175 are allowedto grow laterally in only one direction, this type of expansion allowsthe distance between individual pairs of spacers 175 to be maintainedconstant, while reducing the distance between the constituent spacers ofa pair of spacers 175. As noted above, however, the expansion step ispreferably performed after forming the spacers 175 as freestandingstructures, to facilitate etching of the layer 170.

Also, while “processing” through the various mask layers preferablyinvolve etching an underlying layer, processing through the mask layerscan involve subjecting layers underlying the mask layers to anysemiconductor fabrication process. For example, processing can involvedoping, oxidation, nitridation or depositing materials through the masklayers and onto underlying layers.

Accordingly, it will be appreciated by those skilled in the art thatvarious other omissions, additions and modifications may be made to themethods and structures described above without departing from the scopeof the invention. All such modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

1. A method of semiconductor processing, comprising: providing asubstrate, wherein a temporary layer overlies the substrate and aphotodefinable layer overlies the temporary layer; forming a pattern inthe photodefinable layer; transferring the pattern to the temporarylayer to form a plurality of placeholders in the temporary layer;depositing a blanket layer of spacer material over the plurality ofplaceholders; selectively removing the spacer material from horizontalsurfaces; selectively removing the placeholders relative to the spacermaterial; and expanding a volume of the spacer material, the expandedspacer material forming spacers.
 2. The method of claim 1, whereinselectively removing the placeholders comprises: depositing a fillermaterial over and around the spacer material; and subsequentlysimultaneously etching the filler material and the temporary layer. 3.The method of claim 2, wherein depositing a filler material comprisesdepositing photoresist.
 4. The method of claim 1, wherein selectivelyremoving the placeholders forms a pattern of free-standing spacers andwherein expanding the volume of the spacer material is performed afterselectively removing the placeholders.
 5. The method of claim 1, furthercomprising: providing one or more masking layers under a level of thespacer material; transferring a pattern defined by the spacers to theone or more masking layers; and transferring the pattern defined by thespacers to an underlying substrate.
 6. The method of claim 1, whereinexpanding the volume of the spacer material is performed beforeselectively removing the spacer material from horizontal surfaces. 7.The method of claim 1, wherein expanding the volume of the spacermaterial is performed after selectively removing the spacer materialfrom horizontal surfaces and before selectively removing theplaceholders.
 8. The method of claim 1, wherein the temporary layercomprises amorphous carbon.
 9. The method of claim 8, wherein thephotodefinable layer comprises photoresist.
 10. The method of claim 9,wherein forming a pattern in the photodefinable layer comprisesperforming photolithography and subsequently isotropically etching thephotodefinable layer.
 11. The method of claim 9, wherein a hard masklayer separates the temporary layer and the photodefinable layer. 12.The method of claim 1, wherein depositing a blanket layer of spacermaterial comprises depositing a layer of silicon by chemical vapordeposition.
 13. The method of claim 12, wherein expanding the volume ofthe spacer material comprises forming silicon oxide.
 14. The method ofclaim 12, wherein selectively removing the spacer material fromhorizontal surfaces comprises anisotropically etching the silicon layer.15. A method of semiconductor processing, comprising: defining aplurality of spaced-apart placeholders using photolithography; blanketdepositing a layer of spacer material on the placeholders; etching thelayer of spacer material to define spacers on sidewalls of theplaceholders; subsequently selectively removing the placeholders;expanding a volume of the spacer material forming the spacers; providinga photodefinable layer extending over the spacers; and patterning thephotodefinable layer.
 16. The method of claim 15, wherein expanding thevolume of the spacer material comprises converting the spacer materialto a material having a larger volume than the spacer material, whereinexpanding the volume is performed before subsequently selectivelyremoving the placeholders.
 17. The method of claim 15, wherein expandingthe volume of the spacer material is performed after subsequentlyselectively removing the placeholders.
 18. The method of claim 15,wherein expanding a volume of the spacer material comprises exposing thespacer material to an oxidant.
 19. The method of claim 15, whereinexpanding a volume of the spacer material comprises exposing the spacermaterial to a nitrogen-containing precursor.
 20. The method of claim 15,wherein defining a plurality of spaced-apart placeholders usingphotolithography comprises: providing a layer of photoresist over alayer of temporary material; patterning the photoresist; transferring apattern in the photoresist layer to the layer of temporary material todefine the placeholders; and removing the photoresist.
 21. The method ofclaim 15, wherein a pitch of the spacers is about 100 nm or less.